The present invention relates to an improved process for preparing activated carbon from urban waste, and to activated carbon prepared thereby.
The increasing amount of urban waste produced daily has brought forth the need to find improved solutions to the conventional waste disposal methods of landfilling and incineration.
A large scale improved solution currently applied is the recycling for re-use of certain components of the waste, such as metals, glass and plastics. However, this type of recycling does not provide a solution for a major component of the waste, viz., waste from botanical sources (wood scrap, fruits, vegetables, food, vegetation etc.) and paper product waste, which together with plastic waste constitute the organic fraction of urban waste. An effective solution for the recycling of the organic fraction of urban waste is the use of said fraction as raw material in conversion processes which convert organic waste into economically valuable products. Such a process is a pyrolysis which thermally converts organic waste to charcoal, as a primary product, and to other by-products known as pyrolytic gases and liquids, which have a low commercial value.
U.S. Pat. No. 4,077,847 discloses a solid waste disposal system which sorts urban waste and produces via flash pyrolysis char and pyrolytic oils from the organic fraction of the waste. EP 69,159 discloses a pyrolysis process for organic waste which produces charcoal and pyrolytic products, which are recycled for use in the pyrolytic process. The charcoal produced in pyrolytic processes can be used as raw material for preparing active carbon. The charcoal produced in the aforementioned processes, however, has a high ash content, and therefore the active carbon produced from such charcoal is characteristically soft and brittle and of poor quality.
Among the characteristics which determine the quality of active carbon are the ash content, the pore volume and the hardness. Active carbon which is hard, contains a low percentage of ash and has high pore volume is considered to be of high quality. The ash content of the charcoal produced by pyrolysis directly influences the quality of the active carbon prepared from the charcoal. Charcoal containing 10-20% ash is considered to be excellent quality charcoal. Thus, the active carbon prepared from this charcoal is also of prime quality.
It is a purpose of the present invention to provide an improved pyrolytic process of urban waste.
It is a further purpose of this invention to introduce an improved process for the preparation of charcoal of low ash content, from urban waste.
It is a further purpose of this invention to provide an improved process for the preparation of active carbon.
It is still a further purpose of this invention to provide an improved process for the preparation of granulated active carbon of low ash content, from urban waste.
It is yet another purpose of this invention to provide an improved process for the preparation of granulated active carbon of high quality, from urban waste.
Other objects of the invention will become apparent as the description proceeds.
According to the present invention the organic fraction of urban waste is converted to active carbon via an improved pyrolytic process. The active carbon produced has a low ash content, high pore volume and hardness. Hence, the active carbon of the present invention possesses superior characteristics.
In one aspect, the invention is directed to a process for the preparation of active carbon from urban waste comprising the steps of:
a) Sorting the waste to remove foreign materials;
b) Reducing the size of the waste particles;
c) Drying the waste under anaerobic conditions at a temperature comprised between about 100xc2x0 C.-150xc2x0 C.;
d) Pyrolysing the waste of step (c) at a temperature of about 140xc2x0 C. and above;
e) Granulating the product obtained in step (d) above;
f) Carbonizing the granules obtained in step (e) above under anaerobic conditions at a temperature of about 110xc2x0 C. and above;
g) Activating the carbonized granules of step (f) above in the presence of steam and combustion gases at about 750xc2x0 C.-900xc2x0 C.; and
h) Purifying the activated granules of step (g) above by rinsing in an aqueous acidic solution, and subsequently drying the activated carbon until the water content of the particles is in the range of 4%-8%.
Unless otherwise specifically indicated, all percentages given herein are by weight, and all ratios between various process components are also by weight.
The urban waste referred to herein includes various types of waste produced in the urban environment. For the purpose of this invention urban waste is defined as waste which includes domestic waste and commercial waste but does not include industrial waste. In this context, domestic waste includes waste produced in an average normal household which comprises food waste, paper products and packaging, plastic products, wood, glass and metal. Commercial waste is the waste produced by the commercial sector. Much of the commercial waste is generated by food establishments, markets, grocery stores and the like.
By xe2x80x9cforeign materialsxe2x80x9d it is meant to indicate non-pyrolyzable materials, such as metal and glass, that may interfere with the process.